Process for making colored prints



v 2,218,001 PATENT OFFICE PROCESS FOR MAKING COLORED ram'rs Alan M. Gundelfinger and Lync s. Trimble, Los

Angeles, Calif., assignors to Cinecolor, Incorporated, LosAngeles, Calif., a corporation of California No Drawing. Application August 2, 1938, Serial No. 222,636

12 Claims.

Our invention relates generally to color photography, and more particularly to color processes of the* type wherein two or more colored images are superposed in different strata of an emulsion which is on one side of a film base.

While our invention is equally applicable to three-color photography, it finds its simplest embodiment in what is known as two-color photography, and we will therefore describe a preferred form of our inventionas applied'to this more simplified type of process.

For producing a two-color print, an ordinary film may be employed having a light sensitive emulsion on one side of the base, in which emulsion two color-value images are produced and colored substantially complementary colors to give a finished photograph. A light restraining dye is preferably incorporated in the emulsion to facilitate the production of the two images in different strata of the emulsion. It will be understood that if, as .is usually the .case in motion picture work, it is desired to print a sound track on one edge of the film, it can be colored with one or more colors as desired without modifying the process of our invention.

Suitable color-value negative images may be obtained by any one of various means, two negative images being required fora two-color process, and three negatives being desirable for a threecolor process, the color values-being appropriately correlated to produce a satisfactory picture in substantially natural colors.

In the process of our invention, the red-recording negative is printed to the positive film, either to the face of the emulsion or through the base, as desired, although practical considerations usually make it more desirable to print this first negative to the face of the emulsion, thus producing a color-value image in the outer stratum of the emulsion.

The image is then developed in the usual manner, and washed,'but not fixed, it being usually advisable to have the water used in washing the developed image slightly acid to arrest development. If desired, the film can then be run into a hardening solution, such as a l potassium alum solution or a solution of formalin to harden the emulsion slightly before further treatment. 1

The film is then toned with a suitable iron tone to form a Prussian blue image, a satisfactory solution for this purpose being the following:

Ferric ammonium oxalate grams 6 Potassium ferricyanide do 6 Ammonium chloride do 10. Hydrochloric acid (conc.) cc 5 Water to make er 1 it being undrstood that Prussian blue is ferric ferrocyanide and/or a double salt of ferric ferrocyanide and an alkali metal ferrocyanide.

After the film has been toned to the desired color, it is washed with water, and at this stage We have an emulsion layer containing a blue image, preferably restricted to the outer stratum of the emulsion, with light sensitive salt, for exsensitivity prior to this treatment, and that usually a second image can be printed therein by using printing lights of suitable intensity.

In former color processes of this type where the first image is colored prior to production of the second image, it has been customary to leave the first image substantially unchanged during the subsequent steps of resensitizing the film, producing the second image and coloring it; We have found however, that this former procedure presents numerous difficulties which render it impossible to produce color prints which are commercially satisfactory. For instance, when the Prussian blue image is immersed in the solution used for developing the second image, a portion of the iron salt is reduced resulting in a loss of ferrocyanide ions, which condition causes the ultimate image to be too thin for good projection. We have also found that ferric ferrocyanide has a desensitizing action on the emulsion immediately adjacent to the image, so that there will always be a slight halo of unexposed emulsion surrounding the blue toned image.

To obviate these difficulties, we convert the Prussian blue image to a'ferrichydroxide image by treating the film with a solution containing hydroxyl (OH) ions,,a suitable bath for this pur-' pose being a 2% solution of sodium carbonate or some other salt of .a strong base and a weak acid. If desired, the OH ions may be supplied by a hydroxide of suitable character. We have found that the frric hydroxide image besides being easierto print through (if that be necessary) is not reduced by the subsequent developing of the second image, andthat there is no desensitizing effect on the emulsion surrounding the hydroxide image. Furthermore, the alkaline bath used to convert the image to its hydroxide form has a definite-resensitiz'ing effect on the unexposed light-sensitive salt in the emulsion, so that it is revived sufliciently to readily receive the next image to be printed. If additional or other resensitizing agents are desired, they may be added to the alkaline solution, or may be applied subsequently, so long as the pH of the subsequent solutions is kept above approximately 3.8 at which point the hydroxide dissolves out. Inasmuch as the silver salt, i. e., silver halide or silver ferrocyanide, formed with the ferric ferrocyanide in the first instance, will be reduced to silver in any subsequent developing steps whether reexposgd to light or not, it is fixed out during or after the conversion of the Prussian blue to hydroxide, as by the addition of a small amount of hypo to the alkaline bath or by subsequent treatment with a weak hypo solution (not more than 2%) which will not materially dissolve out the unexposed light-sensitive salt. In this connection, we have found that unless the silver salt is fixed out during or after the conversion of the Prussian blue to ferric hydroxide, the fixation will not be complete due to the fact that the silver salt is occluded in the ferric ferrocyanide image, and this occluded salt will be reduced to free silver in the development ofthe subsequently produced image or images as stated above, which condition of course renders the blue image susceptible to contamination by subsequent color treatments.

After the Prussian blue image has been converted to the hydroxide, the film is washed and dried and isready for the second printing. The second color-value negative is then printed to the positive emulsion layer, in register with the blue image, preferably through the base to restrict it to a different stratum from that occupied by the blue image, and the film is developed and washed in the usual manner. Inasmuch as the solubility product of ferric hydroxide is very small (1.l 10- it is substantially unreduced by the developer.

After the second image has been developed and washed, it may be fixed, but the film is prefer ably subjected to the action of'a treating solution which will rejuvenate or convert the first image back to Prussion blue. Our preferred method of performing this step is to first treat the film with an alkali ferrocyanide such as a 2% potassium ferrocyanide solution which may have a small quantity of formalin in it to harden the emulsion, and then to treat the film with an acid such for example as a 1% solution of hydrochloric acid which may contain about l /2% alum. The acid of course dissolves the ferric hydroxide and the ferric ions immediately combine with the ferrocyanide ions present in the emulsion due to its treatment in the bath of potassium ferrocyanide, to precipitate Prussian blue in situ, it being noted that the film is preferably left in the potassium ferrocyanide solution for a sufiicient time to thoroughly saturate the emulsion therewith. before passing into the acid solution.

The potassium ferrocyanide solution may be combined with the acid solution if desired, so that the rejuvenation can be effected by treatment with but one solution, although from a practical commercial standpiont, we have found that this is not advisable since the ferrocyanic acid in the combined solution has a tendency to decompose, whereas when the ferrocyanide and the acid are kept separate, the solutions are stable. It will be understood, therefore, that when in the claims we speak of treating said film with an alkali ferrocyanide and an acid that we mean to include both. the one-step and the two-step treatment above described.

After the blue color has been brought back to -not affect the previously colored blue image, and

we have found that a Prussian blue image is immuneto most solutions used in coloring. For instance, the film may be subsequently treated with a uranium toning solution to color the second image red by the production of a uranyl ferrocyanide image, or it may be bleached (with an iodide bleach for example) and dyed with suitable basic dyes. Other methods for colorin the second image may also be used, so long as the particular solutions employed do not react with or contaminate the ferric ferrocyanide image.

While as mentioned, we prefer to rejuvenate the Prussian blue image before coloring the second image, it is possible to perform the steps of ,coloring the second image before reconverting the'iron image if the pH of the subsequent solutions is kept above approximately 3.8 so as not to dissolve the hydroxide, and it is to be understood that the claims are meant to include coloring the second image before or after rejuvenating the first image.

If it is desired to produce what is termed a three-color photograph, the first two images may be produced as hereinabove described using appropriate colors, and the third image may be produced in an emulsion layer on the other side of the base. Or a plural strata emulsion may be used and the third image may be produced by any one of numerous methods, as by toning, dyeing, imbibition, etc. It is to be understood that our invention is not limited to any particular method for producing the second or third images, but comprehends only the production of a first image, toning that image, converting the toned image to its hydroxide form, printing and developing a second image, and rejuvenating the first image either before or after coloring the subsequent image or images as the case may be.

While hypo as generally used in the art refers to a solution of sodium thiosulphate, we have used it herein in a moregeneric sense as indicating any suitable fixing agent such for example as any of the alkali metal thlosulphates, cyanides, thiocyanates, and the like which will form soluble complex silver ions, so that all silver can be removed from the film.

While our preferred method is as hereinbefore set forth, it will be understood that the Prussian blue image can first be reduced to its ferrous form and converted to ferrous hydroxide, which can subsequently be oxidized to ferric hydroxide, which is then rejuvenated to Prussian blue as before. Or the ferrous hydroxide can be converted to a ferrous salt which can be oxidized to Prussian blue,

From the foregoing, it will be seen that we have disclosed a process for coloring film which provides a simple and easy method for producing a colored first image before the second image is formed in the emulsion, with the consequent elimination of the problem of accurate control of the penetration of treating solutions which is present when both of the images are developed up before the coloring treatment. Likewise, we have developed a rapid and eflicient method for reconditioning the film for the production of a second image therein, and preserving the first image which is highly practical for commercial production, and while we have given specific examples of constituents and concentrations, it is to be to a Prussian blue image by treatment with an iron toning solution; then treating said film with a solution which converts said Prussian blue image to an iron hydroxide; then producing a second image in said film in superposed relationship with said first image by printing from another of said negatives and developing the latent image obtained thereby; then converting said first image back to its original color; and coloring the second image a color different from that of the first image.

2. A method as defined in claim 1 in which said first image is converted back to its original color by treatment with an alkali ferrocyanide and an acid.

3. A method as defined in claim 1 in which said first. image is converted back to its original color by treatment with potassium ferrocyanide and an acid.

4. A method as defined in claim 1 in which said first image is fixed dining or after its conversion to iron hydroxide, by a solution which does not appreciably fix out the unexposed silver salt in said film.

5. The steps in a process for coloring photographic images which comprise: producing a Prussian blue image in a stratum of emulsion; converting said image to iron hydroxide; then producing a secondimage in said emulsion in register with said first image and subsequently reconverting said first image to Prussian blue.

6. The steps in a process for coloring photographic images which comprise: producing a Prussian blue image in a stratum of emulsion; converting said image to ferric hydroxide; then producing a second image in said emulsion in register with said first image and subsequently reconverting said first image to Prussian blue.

7. A method as defined in claim 5 in which said solution for converting the Prussian blue image to iron hydroxide contains a small amount 01' hyp 8. The method of making a color photographic print from suitable color-value negatives which includes: printing one of said negatives to a positive film; developing the latent image obtained thereby; coloring said image with an iron toning solution to produce a Prussian blue image containing a silver salt; then treating said film with an alkaline solution containing a small quantity of hypo to convert said metallic salt image to an iron hydroxide image, to fix out said silver salt and to resensitize said film; then producing a second image in said film in supe sed relationship' with said first image by printing from another of said negatives and developing the latent image obtained thereby; and then converting said first image back to Prussian blue by treatment with an alkali metal ferrocyanide and an acid.

9. A method as defined in claim 8 in which said film is treated with hypo immediately after the conversion of said first image to iron hydroxide.

10. The method of making a colored photographic print from suitable color-value negatives which includes: printing one of said negatives to a positive film; developing the latent image obtained thereby; converting said image to a Prussian blue image by treatment with an iron toning solution; then treating said film with a solution which converts said Prussian blue image to a. ferric hydroxide image; then producing a sec-- ond image in said film in superposed relationship with said first image by printing from another of said negatives and developing the latent image obtained thereby; then converting said first image back to Prussian blue; and coloring the second image a difierent color from that of the first image.

' 11. The method of making a colored photographic print from suitable color-value negatives which includes: printing one of said negatives to I which converts said Prussian blue image to ferrous hydroxide; then producing a second image in said film in superposed relationship with said first image by printing from another of said negatives and developing the latent image obtained thereby; then converting said'first image back to Prussian blue; and coloring the second image a color different from that of the first image.

12. The method of making a colored photographic print from suitable color-value negatives which includes: printing one of said negatives to a positive film; developing the latent image obtained thereby; coloring said image with an iron toning solution to produce a Prussian blue image containing a silver salt; then treating said film with an alkaline solution containing a small quantity of hypo to convert said Prussian blue image to a ferric hydroxide image, to fix out said silver salt, and to resensitize said film; then producing a second image in said film in superposed relationship with said first image by printing from another of said negatives and developing the latent image obtained thereby; and then converting said first image back to Prussian blue by treatment with an alkali metal ferrocyanide and an acid.

LYNE s. 'mmnm. 

